Mono- and oligo-vesicular synapses and their connectivity in a Cnidarian sensory epithelium (Coryne tubulosa).

The spherical end-knobs of the tentacles of capitate hydropolyps are an evolutionarily early paradigm of a chemo- and mechanosensory epithelium composed of four types of sensory cells and one type of chemo-mechanosensitive nematocytes (stinging cells), all separated by supporting cells. The epithelium discriminates sites and compositions of stimuli and induces various kinds of behavior. Recent electrophysiological studies demonstrated rapid chemo-synaptic signal transmission of nematocytes and mechanosensory hair cells, graded in amplitude and duration. The present electron microscopic work, applying serial sectioning, analyses the ultrastructural basis of signal transmission and efference control in the tentacular spheres of Coryne tubulosa, a species also used in preceding studies. Neurites of sensory cells and of proximal ganglion cells constitute a nerve plexus at the base of the ectodermal cells. No ganglion cells are located within the spheres. Chemical synapses of the usual configuration connect neurites or are efferent to nematocytes and hair cells. Each of these synapses contains only 3-10 clear and/or dense-core vesicles of 70-150 nm diameter (oligo-vesicular synapses). For the graded afferent signal transmission of nematocytes and hair cells, the only candidates are regularly occurring zones of neurite contacts at the base of these cells. At their presynaptic side, mostly one (more seldom two to four) large vesicles (160-1100-nm-diameter magno-vesicles) are attached to a surface membrane density. In order to reconcile structural and functional data, a transient fusion and partial depletion of stationary vesicles is considered for the release of transmitter in mono-vesicular synapses, similar to recent findings for vertebrate endocrine secretion. The same principle is discussed for the usual oligo-vesicular synapses of Cnidaria.

Variations of concentric hair cells in a Cnidarian sensory epithelium (Coryne tubulosa).

In capitate hydropolyps, the spherical end-knobs of the short tentacles present an exceptional concentration of sensory functions in one of the evolutionarily oldest nervous systems. The tentacular spheres are the basis of sensation and discrimination of objects and of capturing of prey-objects by the discharge of nematocytes (stinging cells). Recent electrophysiological studies of the spheres revealed combined chemo/mechanosensory functioning of the nematocytes and mechanosensitivity of further types of cells. The present electron microscopical study made use of the small size of the spheres of Coryne tubulosa to characterize all cells of some spheres. Five types of ectodermal cells were found to have sensory structural features and to be separated by or enclosed in supporting cells: 1) nematocytes of the stenotele type; 2) short and 3) long ciliated concentric hair cells, which carry a cilium-stereovilli bundle, similar to the cnidocil apparatus of nematocytes; 4) cells having a recessed cilium-microvilli complex equipped with a thick cell-traversing rootlet (rootlet cells); and 5) cells having a recessed short cilium with no microvilli and only a short rootlet and containing, apically as well as basally, aggregations of dense-core vesicles (vesicle-rich cells). Types 1-4 vary the configuration of a concentric cilium-microvilli complex (variations of a concentric hair bundle) and were demonstrated or inferred to be mechanosensitive. Apical exocytotic activity, which is well known for the nematocytes (discharge of their cnidocyst), is indicated by ultrastructure for the nematocyte-resembling concentric hair cells and for the vesicle-rich cells. The tentacular spheres are considered an early paradigm of a sensory epithelium. Its synaptic structures and extensive connectivity are the subject of a subsequent paper.

I'm running on insulin. Summary of the history of the International Diabetic Athletes Association.

The changes that physical activity brings in the functioning of the human body have a special interest to active individuals with diabetes. Certain adjustments in dosing are necessary. Even today, with such an emphasis on healthy life-style, little information is available to assist an individual with diabetes to exercise safely. Granted, no easy formula exists. Many different factors influence blood glucose. Most often, individuals with diabetes learn by trial and error how to best manage their favorite activity. In 1985, Paula Harper founded the International Diabetic Athletes Association (IDAA) in hopes of educating people with diabetes about the benefits of regular exercise. For most individuals with insulin-dependent (type I) diabetes mellitus, it is not encouragement, but safety that is the issue. The IDAA offers great opportunities for sharing ideas at its annual meetings. These meetings attract an exceptional faculty of speakers and offer a mix of workshops led by experienced diabetic athletes on various sports. A quarterly newsletter is published that presents new information and recognizes success stories. IDDA chapters exist in the U.S., Canada, U.K., Germany, France, Luxembourg, Switzerland, Belgium, the Netherlands, and Spain.

High frequency radial movements of the reticular lamina induced by outer hair cell motility.

Recently, it was shown in cochlear explants from the guinea pig cochlea that electrokinetic motile responses of outer hair cells can induce radial and transverse motion of the reticular lamina. Here we demonstrate, that the radial component of these motions can be measured up to high frequencies (15 kHz). Cochlear explants were taken from guinea pig inner ears and exposed to a sinusoidal electric field. A double photodiode was used as a linear position detector with high spatial and temporal resolution to detect radial movements in the plane of the reticular lamina. The organ of Corti of the second, third and fourth cochlear turns was stimulated with frequencies of the electrical field between 0.5 Hz and 20 kHz. Sinusoidal movements of up to 15 kHz were recorded. At higher frequencies the signal-to-noise ratio became too small. The largest responses were measured at the three rows of outer hair cells. If the strength of the electrical field was 2 kV/m, into which the cochlear explants were placed, the amplitudes of outer hair cell movements were around 1 micron at 1 Hz and 10 nm at 10 kHz. Uncoupling of the outer hair cells from the tunnel of Corti and from the inner hair cells decreased the oscillations of inner hair cells but did not affect outer hair cells. The movements showed frequency dependent amplitudes like a complex low-pass filter but no best frequency was observed.

Spontaneous and electrically induced movements of ampullary kinocilia and stereovilli.

In the transparent vestibular organ of young eels, isolated in toto, movements of individual kinocilia and hair bundles of the frontal ampulla were recorded by photodiodes and a video system. Flagella-like oscillations of kinocilia occurred spontaneously when preparations deteriorated and could be induced regularly in fresh preparations by pressing onto the tip of the cilium. Upon step-like electrical polarization of the epithelium hair bundles deflected in a tonic, pointer-like manner. When the apical membrane was hyperpolarized the hair bundles deflected towards the kinocilium (positive deflection) amounting to about 0.6 degrees when the polarization was made strong enough to cause saturating responses in the ampullary nerve. In response to sinusoidal voltage the amplitude of the hair bundle deflection declined by -4 dB/octave for frequencies above 1.3 Hz. When the kinocilium was disconnected from the bundle of stereovilli by transient reduction of divalent cations, voltage induced deflections occurred, of both the kinocilium and the stereovilli. Reducing the extracellular Ca-activity seemed to destabilize the electrically induced deflections; blocking the oxidative metabolism (CN-) had no effect. The induced deflections only disappeared upon chemical fixation by glutaraldehyde or treatment with triton X-100. Surface tension and electrostriction of the cell membrane are discussed as possible force generators.

Cupula displacement, hair bundle deflection, and physiological responses in the transparent semicircular canal of young eel.

The transparent labyrinth of young eels (Anguilla anguilla L.) was used in toto for studying the configuration of cupula displacement, deflection of the hair bundle, and correlated changes in transepithelial voltage (delta TEV) and nerve activity (delta NA) in the semicircular canal. Microcapillaries were introduced into the canal through holes produced by a microthermocauter. Mechanical stimulation was applied either by injection of fluid into the ampulla or by electromagnetically displacing ferrofluid as a piston within the canal. Motion of individual kinocilia, stained cupulae or the ferrofluid piston was analysed by double-exposed microphotographs, photodiodes, or a video-system. The three-dimensional cupula displacement configuration was found to be piston- to diaphragm-like. Hair bundles at different sites on the crista exhibit differences in amplitude and time course of deflection. The transfer factor between shifts of the canal fluid and the tips of the kinocilia is 0.4-0.6. Displacements in opposite directions induce delta TEV and delta NA of opposite sign. Various tests confirmed delta TEV to reflect receptor potential responses. Nerve activity adapts to a tonic response with a time constant of 6.4 s. No similar adaptation occurred in delta TEV. Stimulus-response curves of TEV- and NA-responses are similar and sigmoid in shape with saturation at ciliary deflections of roughly +6 degrees and -3 degrees.

Passive and active deflections of ampullary kinocilia correlated with changes in transepithelial voltage.

Deflections of individual ampullary kinocilia were optically recorded in the undissected vestibular system of young eels. At mechanical stimulation, transepithelial receptor potentials and nerve activity were recorded. Saturating responses occurred at ciliary deflections of +6 degrees and -3 degrees. Kinocilia occasionally oscillate spontaneously in a snaking or pointer-like mode as the preparation deteriorates. In nearly all kinocilia of fresh preparations exogenous transepithelial voltage change induces active pointer-like deflection in a graded and tonic manner. A voltage change of a given sign induces a deflection that counteracts mechanical stimuli producing a voltage change of the same sign.

Chemical dissection of stereovilli from fish inner ear reveals differences from intestinal microvilli.

A quick method was developed for isolating the stimulus-receiving apparatus (stereovilli = 'stereocilia') from the vestibular apparatus of fish (Scardinius erythrophthalmus and Rutilus rutilus) in sufficient quantity and purity to study the solubilities and stabilities of their structural elements by electron microscopy. The stereovilli were adsorbed to a support and, after various treatments, negatively stained or metal shadowed after freeze drying. For comparison, and in order to ensure the validity of the method, some experiments were similarly performed on intestinal microvilli from chicken. Microvilli adsorbed to a support gave similar results as in suspension. Stereovilli and microvilli are similar in their architecture, except for the specialized base of stereovilli, and in the Mg2+- or Ca2+-induced splaying of the actin cores. Major differences occur in the solubilities of the linkers which connect the actin core and the membrane (a-m-linkers). In contrast to microvilli, these linkers are removed from the stereovilli core together with the membrane by Triton-X-100. The linkers together with some membrane components are preserved by glutaraldehyde fixation prior to detergent extraction. In stereovilli, the position of the linkers is recognizable in fixed material. In microvilli the membrane contains so much material, which becomes detergent insoluble after glutaraldehyde fixation, that the linkers become completely obscured.